1. Field of the Invention
This invention relates to liquid-crystal electronic technology and more particularly to methods and articles for use in manufacturing and handling liquid-crystal displays.
2. Prior Art
A liquid-crystal display, hereafter referred to as LCD, is essentially a light valve controlled by an electric field impressed across the LCD. Depending on the arrangement of the components of an LCD and on the strength of the applied electric field, light impinging on one face of the LCD will be largely transmitted, partially transmitted, or largely not transmitted through the LCD. This characteristic has many useful applications. By arranging an LCD so that light is transmitted through certain parts of the LCD but is not transmitted through other parts, the LCD can be utilized to show pictures or alphanumeric characters. For example, LCD's are used to show the time of day in electronic watches and to show various types of information in calculators.
An LCD is typically made by sandwiching liquid-crystal material between two glass plates. The glass plates are so treated that the liquid-crystal molecules nearest the plates have preferred orientations relative to the plates in the absence of an electric field. Transparent electroconductive coatings are formed on the inside faces of the glass plates, i.e., the faces directly adjacent to the liquid-crystal material. Leads are attached to the two electroconductive coatings, and an external electric power source is connected to the leads so that an electric field can be applied across the liquid-crystal material in the LCD.
To create the contrast between the areas of an LCD through which polarized light is transmitted and those areas through which polarized light is largely not transmitted, light polarizers are placed over the outside faces of the glass plate. The two polarizers may be arranged so as to have their polarization directions parallel to each other, perpendicular to each other, or at some intermediate angle to each other. Going from one side of an LCD to the other, the components of the basic LCD then are a polarizer, a glass plate with an electroconductive coating on its inside face, a slice of liquid-crystal material, a second glass plate with a second electroconductive coating on its inside face, and a second polarizer.
Goldmacher et al. in U.S. Pat. No. 3,499,702 describes one embodiment of an LCD. In brief, light passing through the first polarizer is plane polarized. In the absence of an electric field, the plane of polarization of the light rotates through a predetermined angle as the light passes through the liquid-crystal material. This angle of twist is established from the internal orientations of the liquid-crystal molecules. As the light reaches the second polarizer, the light is largely transmitted, partially transmitted, or largely absorbed by the second polarizer, depending on the orientation of the second polarizer relative to the first. If an electric field of sufficient strength is applied across the liquid crystal material, the liquid-crystal molecules reorient themselves in such a manner that light passing through the first polarizer maintains the same plane of polarization as the light passes through the liquid-crystal material. Thus, light reaching the second polarizer is transmitted or absorbed in amounts different than the amounts absorbed when no electric field is applied. By applying an electric field across certain regions of an LCD but not across other regions, this phenomenon permits an LCD to show a time-varying picture in which some areas are dark and others are light.
A substantial amount of prior art exists in the manufacturing of LCD's. Herein, we are concerned with the prior art dealing with the application of polarizer material to partially-finished LCD's and subsequent handling of the LCD's.
In the prior art, two principal methods have heretofore existed for applying polarizer material to partially-finished LCD's. In one method, standard polarizer material is cut to the appropriate size to cover the active area of a single LCD. Typically, the polarizer material is cut with a die-cutting machine. An operator then deposits one piece of polarizer material into an alignment cavity, places a partially-finished LCD over the first polarizer, deposits a second polarizer over the LCD, and finally clamps the combination together. The second method is substantially similar to the first method except that polarizer material having a transparent adhesive coating on one side is used in lieu of standard non-adhesive polarizer material. By using adhesive polarizer material, the clamping step is eliminated.
There are a number of disadvantages with the prior art methods for applying polarizer material to partially-finished LCD's. In either prior art method, the operator works on each LCD individually. That is, the operator combines the partially-finished LCD's with the polarizers one LCD at a time. This procedure is inefficient because it takes substantial time for the operator to work on the LCD's individually. Since the LCD's are individually assembled by hand, substantial care must be taken to prevent dirt and bubbles from getting between the glass plates and polarizers and to assure the polarizers are properly aligned with the glass plates. In short, the manual nature of the prior art methods is undesirable because it is highly time consuming and requires a high degree of care to keep the number of unacceptable LCD's at a low level.
A further disadvantage is the inefficient utilization of expensive polarizer material in the prior art methods. The mechanical dies used to cut polarizers from polarizer sheets have about 0.1 inch of material between individual polarizers. As a result, utilization of polarizer sheets is usually not much better than 70% and often much lower. At today's rates, the cost of polarized material actually used in an LCD is around 3% of the total retail price of an LCD. This means that 1-2% of the total cost of an LCD goes into wasted polarizer material.